Method of fusion welding involving use of initial layer of finely divided metal



May 11, .1948. E. F. WILSON ET AL METHOD 0F FUSION WELDING INVOLVING USEOF www lll/ll Filed Sept. l, 1942 INITIAL LAYER OF FINELY DIVIDED METALINVENTORS Evan -l/l/i/son, John C. Gru bb Id -/ogd HJW/er1 ATTORNEYPatented May 11, 1948 METHOD OF FUSION WELDING INVOLVING' USE OF INITIALLAYER OF FINELY DI- VIDED METAL Evan F. Wilson, Akron, and John C. Grubband Floyd A. Fowler, Barberton, Ohio, assignors to The Babcock & WilcoxCompany, Jersey City, N. J., a corporation of New Jersey ApplicationSeptember 1, 1942, Serial No. 456,856

This invention relates to the fusion welding of metal plates andsections wherein the welding surfaces of the parts being welded arearranged in abutting relation to `provide a groove for the re- A ceptionof Welding metal.

In conjunction with such Welding, commonly referred to as butt-welding,it has been customary to back-up the welding groove with a member whichwill inhibit the flow of Weld metal therefrom while in a molten state,and for this purpose, metal strips or rings have been used which becomewelded in place. This is ordinarily objectionable and their removaloften requires considerable effort and expense by chipping or machining.If left in place, particularly in the case of tubular bodies, suchstrips or rings obstruct the flow of the medium conveyed and interferewith either visual or radiographic inspection.

Certain varieties of more readily destructible backing members have beendeveloped but these have in general been unsatisfactory due to thematerials used and other factors which have resulted in contamination oithe weld metal of the joint.

In the development of the present invention it has therefore been ourbroad object to overcome the deficiencies of prior practices, using newmethods, and new apparatus if necessary, so as to assure maximum controlover the quality of the joint metal, with minimum attention orinconvenience on the part of the operator.

A more specic object of the invention contemplates a backing member ofsuch characteristics that it may readily be removed from the Weldingzone when desired, and one that by suitable selection of its materialand formation may be utilized repeatedly for successive weldingoperations either in conjunction with a single seam, or with a pluralityof seams.

Another object is the utilization of a backing material or materialswhich will have no deleterious eiect on the Weld metal within thegroove, but rather will contribute to the production of a sound weldthrough the prevention of slag entrapment.

A further Objectis to enable inspection to be made of the joint at anystage of the operations whereby repairs can `be made if necessary,before a. large amount of metal has been deposited which needs to bechipped out to reach the defect.

Other objects are concerned with the ready manipulation of the backingmember before, during `and after the welding operations, involvingapparatus applicable to vwork pieces of various forms and dimensions.

5 Claims. (VCI. 219-10) With the foregoing objects in view, we'ha'vechosen to use a non-metallic, refractory material as a, backing for thewelding groove, of such character as to withstand the direct heat of theelectric arc, or other source of welding heat, and thus eliminate anytendency for the material to become permanently attached to the work orto have any detrimental eiiect on the quality of the weld metal.

The surface in contact with the work is preferably of carbon, and in oneform may be provided as a coating or layer of graphite on the outersurface of a ceramic body portion or core, formed for example of silicasand suitably bonded and baked, the graphite being applied either as adry'powder, or as a Wash consisting of a graphite-water mixture. Abacking member constructed in this manner may be conveniently formed toany desired shape and may be readily destroyed, if desired, tofacilitate its removal from the working zone after welding. Furthermore,the refractory core is suciently permeable to carry away gases-whichmight otherwise be introduced into the metal. One effect of the carbonlayer is to provi-de an exposed portion more refractory to the heat oiwelding than the inner body portion, the melting point of carbon beingabove 6300 F., practically twice that of the body portion which,although composed of high melting point oxides, would ordinarily becomefused ii directly exposed to the temperatures encountered in welding. VAsecond and more important effect of the carbon surface is to prevententrapment o f slag within the body of Weld metal, the slag otherwisereacting with the minerals of the backing member, if left uncoated, andthus adhering to the member to prevent its flotation to the surface. v

In another form, the backing member may be of solid graphite or carbonwhich has certain advantages in that it may be machined or iiled to thedesired t, and furthermore, if destroyed for purposes of removal, theresidual carbon fragments which are relatively soft Will not seriouslyaffect the operation of valves or other parts susceptible to wear.

While the above forms of backing members are effective in minimizing theentrapment of slag by the substantial elimination of chemical reactionwith the backing material, there is an additional method to be disclosedfor the prevention of mechanical entrapment of sl-'ag'in the weld grooveor where the fit of the backing member against the work offers anopportunity for slag retention.

In accordance with our improved method, with 4 Fig. 3 is a fragmentaryview showing modied application of the invention.

According to Fig. 1, the parts I3 to be welded together are in the formof tubular sections, for

example, shaped at their end edges. I2 to provide lipVV portions I4 atthe bottom of a, welding groove any non-metallic bodies such as slagbeing floated Y to the surface of the molten iron to assure clean metalthroughout the root'of the weld. J

Weld metal is fused into rtheegroove progressively along its lengthsimultaneously with the melting of the iron powder,..the,molten powderand deposited weld metal', combiningfto; form the initial layer at thevbase,--andsubsequent-1li layers being laid down and the welding-.oftheseam completed as described hereinafter.

The powder may be tamped lightly before welding to prevent excessivevoids or looseness,..but without appreciable pressure, otherwise the de-',siredporosity of :themass ywould be reduced. The powder ismeltedrrapidly at -the exposed .surface `of .tl1.el-mass,.duey tothefineness `of its'particles, -thus :forming a molten surface from walltowall of the groove, .and .since.the :massis relatively porous.. and.providespoor thermal Contact, --the .ipenetratlonaof heatthroughrthepowder is ,re-

tardedrdespiteV its rapid surface fusionandin consequence the fusion issuperficial; and. only a Usmall lquantity `of powder. is required.'.fMoreover Ythebead-protruding fromithe underside ofthe nriishedweld is.small which .for tubular .struc-- `tures provides a minimum :amount vofinternal Uobstruction. If-there should be anyindication ofAVcarburlzat-ion of' thesmetal 1 due to the use of a carbon retainer. orbacking, this may be avoided by;increasingtheamount'ofpowder so thatonly a portionls fused. -It-is contemplated that for position'welding,ythat is, otherthanvhorizontal, it

order to hold the powder inplace,` -provided the bondingmaterial isof anonslag-forming character.

i Bure or 'relatively pure ,iron powder of a-neness Vof., approximately100 mesh has been vfound -especiallyeflective for our purpose in theweldingof ferrous metals.4 Steelpowder can also be used, but the ironhas proved more effective, probably becauseof its higher melting point.An advantagein usingpowder is `that itis adaptable toyariousshapes and.sizes ofgrooves, but it is toabefnoted thatinycertaininstances anA ironhfoilfor. a mile steel 4.foil may be substitutedor a :striporotherfshape of suchmetalsor a combinaf tion, of one or more of lsuchforms with powder in suitable proportions. It will beunder-stood. thatalloys of..suitable properties may also be used to provide .the .initialmetallic pool.

-Experimentsfhave indicated that certain other materials,A such asplastics might-beused to re- .place carbon-as thebacking-material,.andsuch substitut-ions are contemplatedas being within ,the ,scope'of thelinvention 4provided there is substantial equivalency in theirproperties-relative fto carbon for which the substitution ismade.

'The various objects andV advantages of the in- .ventiont .and-themanner -inwhich the invention y.may be practiced, arezmorefullydisclosed in the '-detailed `descriptionwhichv follows, andin. the-ac- .-oompanyng drawings-,11n whichlig. Aliis afsectionalelevation of4apparatus `use- :ful intherpractice vof ouriinvention;

Fig. 2 is an end view of parts shown inpFig. 1 :irxsection along line2-2;;a-nd

might be desirable to employ a bonded powder in` i6 adapted to receiveand retain molten welding metal for uniting the parts by fusion. Theparts I may be suitably supported to maintain their relativepositionsasshown, in axial alignment and-.with the lips I4 spaced apart to providea narrow gap I8 of.` approximately one-eighth inch,

. for example,- forplates measuring about two in- .ches in thickness.-shaped at their ends to provide a shallow circum- The parts IU may befurther i fferentialrecessZD formed inwardly of the lips I4 and spanningthe gap I8 to provide a bearing surface for the arcuately surfacedbacking memberf22.' The recess is preferably formed by counterboringeach section I0 to a true cylindrical surface of predetermined diameter,thus correcting for possible Avariations in inside diameters andAeccentricities, of` the sections, in accordance with the knownvariations` permissible in the commercial manufacture of tubularproducts. .Such counterboring assures aclose fit between the`.backingmember 22` and the work at any circumferential location towhich the member may be applied, and enables the same member, ormembers, of a, corresponding predetermined curvature, to be1used.interchangeably with any two correspondingly counterbored sectionsof the same nominaldiameter andthickness, as is desirable in quantityproduction.

For the purposes of kthis invention, the backing member 22 of anon-metallic, refractory material, such as carbon, for example, in blockform and shaped to engage anarc of the cylindrical surfacelZ, is formedwith a groove 24 in itsouter surface -to provide a space suitable forthe size of inside bead desired,f a. depth approximately equal. to the.width of. the gap I8 having been found convenient, and aradius somewhatgreater than the gap dimension.

With the parts Ii) in position for welding as shown in Fig. 1, .thegroovcd block 22 is held in .close engagement withthe under surface ofthe lips I4, preferably by means of a tool or machine, of a type tobedescribed in detail hereinafter, wherebyvthe; block may .-bemovedconveniently into and. outof the welding position, and from vone weldingzone to another, if necessary, as the welding proceeds.

Iron powder ofrelatively pure chemical composition is placed in thewelding groove I6 to a depth-at least level with the top edges of thelips I4,- and preferably to a somewhat greater depth to cover the lips,approximately asrshown at` 25 in Fig. l, prior to introduction of thewelding metal, the powder substantially filling the cavity formed by theblock groove 24.below the lips I4, the gap I8 between the lips, and thebottom portion of the welding groove `I6 above the lips. Welding metalis then deposited within 4the groove I6, by the electric arc weldingprocess, for example, utilizing electrodes of about `one-eighth inchdiameter in the top or down-hand position for` laying down at least thefirst two beads or layers at the base of the groove, in successivelengths or sections throughout the total length -of the. seam. The

vlength, of `each section is preferably somewhat .less than the lengthlof contact surface between sary to shift the carbon member and workrelatively for each additional section to be welded. When weldingcircumferential seams, the length of a section is made small enough topermit welding at all times from the top of the groove. Each section ispreferably completed by the deposition of at least two layers while thebacking-up block is in place for that particular section, for thepurpose of alleviating the danger of the weld metal burning through, thesecond layer of a section being deposited immediately upon the firstlayer of the section, and the multiple-layer deposit being allowed tocool to about 800 F. before shifting the block to a new position andproceeding to lay down the iirst layer of the succeeding section. Whenit is necessary to renew electrodes, thus requiring interruption of thearc, the end of the bead length already deposited is preferably taperedby chipping for a distance of about one-half inch before the succeedingelectrode is started to insure complete fusion and the elimination ofholes or defects caused by restriking the arc. It is desirable to add asmall quantity of iron powder to the chipped area to replace the amountdisplaced as a result of the chipping operation.

After the sections have been completed in the manner just described, tothe extent of providing a continuous weld throughout the length of theseam at the base of the groove I6, the remainder of the groove may befilled with welding metal according to established practices to completethe union of the two parts I 0 of the work.

A desirable feature of this method of welding is that by applying ameta-l powder within the gap I8 between the lips I4 and above the lips,a protective pool of relatively pure metal is provided at the lowermostpoint of the seam and prevents slag from the electrode covering, orresulting from oxidation of the work metal, from being entrapped in thegap where the parts to be welded adjoin, the carbon surface of theretainer 22 effectively preventing the formation of slag from beneaththe gap.

With this method also, it is possible to examine the weld from theunderside at intermediate stages for any defects which may haveinadvertently occurred during the process, and to make repairs beforedepositing additional metal, since the backing member may be readilyshifted or removed to` entirely expose a portion already welded.

After welding, the iron originally in powder form is evident as a small,fairly uniform ridge standing out from the underside of the work, theuse of the highly refractory backing member permitting complete fusionwithout burning through as might be possible with a steel backingelement or metallic backing-up part-s, and because of good fusion theridge and its junction with the work being rounded so that there are nonotching or crack-like effects.

A form of apparatus is shown in Figs. 1 and 2 for adjustably supportingthe refractory backing-up member 22, for example, in relation to acircumferential seam between tubular work pieces I 0. In such anarrangement the outer surface 28 of the member 22 is made arcuate,preferably to a predetermined radius as has already been indicated, forengagement with the counterbored Work surface 2U at the underside of thelips I4. The groove 24 preferably extends throughout the entire lengthof the arcuate surface 28, and beyond' they ends of the surface 28 theblock is recessed as at 30 where holes 32 are provided.

6, to receive pins 34 long enough to extendI through the gap I8 betweenthe work parts Il) to facilitate alignment of 'the groove 24 with thegap, while the block 22 is in contact with the Iwork for welding, asshown, and also while the work is being rotated to an adjacent weldingposition. The pins are removable and both may be used when making theinitial adjustment, whereas for subsequent adjustments, after a sectionvof the weld has been completed and groove 24 is to be aligned with thegap at an adjacent circumferential location, one pin is removed due tointerference with the welded section while the bead formed by fusion ofthe iron powder in that section and extending into the groove 24 servesas a guide in place of the pin. The apparatus for supporting the tubularparts I0 may be of a known type, with rollers, for example, providingfor rotation of the parts for the purpose described.

The backing-up apparatus includes an extensible support adapted to bepositioned inwardly of the parts I0 for holding the block 22 in firmengagement with one wall of the work while transmitting the resultingthrust to the opposite wall, the support being shown in a partiallyextended working position in Figs. 1 and 2.

The upper portion 36 carrying the block 22 is inthe form of a channeland comprises a rectangular bar 38 to which side plates 40 are secured,as by screws 42,*the block 22 resting on the bar 38 and being held inplace by bolts 44 extending through the block and side plates, with nuts46 at their ends. The lower portion comprises a base plate 48 having itsouter edges rounded as at 50 to a radius suitable for the size or sizesof tubular parts with which the support is to be used, the resultingcurved surfaces 50 being grooved as at 52 to provide a clearancefcr theinwardly protruding bead of weld metal which is formed as the weldingprogresses. The recess 20 is preferably made of suitable width toprovide a bearing surface for base plate 48 at one end of the support,in addition to a bearing surface for the backing member 22 at theopposite end, as heretofore described. f

Upper and lower slotted guides 54 and 56 provide an adjustableconnecting strut between the block carrier 36 and base plate 48, theupper guide having outer slotted blades 58 vslidably engaging the singleintermediately positioned slotted blade 60 of the lower guide to enablethe support to be extended and retracted to the extent required formoving the backing-up member 22 into and out of engagement with the worksurface. Each guide-is flanged at one end, and the flanges 62 and 64respectively secured to the block carrier 36 and the base plate 48 byscrews 66 and 68. The guides are slotted longitudinally as at I0 toprovide accommodation for an adjusting wedge member 12 which cooperateswith the cross bars 14 and 16 at the ends of the slots for causing theguides to move relatively and thereby adjusting the amount to which thesupport is extended or retracted. The support is continuously biasedtoward the fully extended position through the action of springs 18which are received at their lower ends in cylindrical guides fixed tothe base plate 48, and which at their upper ends bear against thecarrier bar 38 within the cylindrical4 guides or recesses 82.

A positioner element, denoted generally by the character 84, is providedfor convenience in moving the block-support longitudinally of the work,as is necessary for example when bringing the block 22 vinto registerwith the seam interiorly of a tubular body l0. The positioner 84includes a pin 86 havinga Dor-tionof reduced diameterextending throughthe carrier bar -38 and side plates 40 andheld inplace by nut 90 at itsouter end and by the set screw 92 which engages the flat 94 to preventrotational displacement. A tubular section 96- of the positioner elementis detachably connected to the pin` 86 by means of a removable lockingpin 98having its end inserted through registering holes in thepositioner tube 96and pin 86. A coupling tube. |02 secured adjacent theouter end of the tube 96 provides a socket for a tubular extensionsection |04 secured therein by set screws |06 and having `a. notched end|08 interntting with the end of seetion 96.

The adjusting Wedge l2 by which the elevation of the block 22 isregulated extends through the slots 'l0 in guides. 54 and 56 and isdetachably coupled to an adjusting rod I0 by means of a removablelocking pin 2, similar to pin `98 for the positioner. The rod- ||0 isreversely bent as shown to provide a major straight length portionmovable longitudinallywithin the tubular positioner sections 96 and |04for convenience of manipulation and compactness of assemblyythe section96 being slotted as at ||4 a sulieient distance to make available thefull range of adjustment as determined by the rise ofthe inclined psurface H6', from the fully retracted yposition when the cross bar 14engages the at surface H8 at the high end of the incline tothe fullyextended position when the cross bar Illl engages the flat surface |20-at the low end. The adjusting rod H0 may include an extension piece |22joined to its original length by a coupling |24 and tted'with ahandle-at its outer end, if desired. The length of extension requiredwill be generally determined by the dimensions of the work, and variouslengths may be used to suit various'work piece dimensions, the sameapplying to the length of extension provided for the positioner element84.

Fig. 3 shows' a modied applicationfof the invention wherein the workpieces |26 are represented as flat plates havingv ends shaped`andarranged to `provide a longitudinal groove similar incross-section-to the circumferential groove I6 in Fig. l, with lipsUl'separated by a gap I8a as in the previous embodiment. The refractory`backing-up block or bar '|28 oi carbon, for example, having a groove24a in its upper surface, is supported in a metal trough or channel |30against the underside of the lips |48, with the groove 24a in alignmentwith the gap |8a. It will beunderstood that the plates |26 maythemselves be independently supported by suitable known devices, Whileproviding a separate adjustablesupport for the Ablock carrier |30diagram'n matically indicated at |32, for advancing and retracting :thebloei-r- |26 relative to the Werl: |26, the number of supportingelements |32 and their positions being varied as required. The weldingprocedure is as previously detailed, the iron powder being placed in theWelding groove iiil to a level suflicientto at least ll the gap I8e andpreferably somewhat higher to cover adjacent portions of the lips Ma,and the weld metaldeposited throughout the length of the groove at'itsbase, with the backing-up member in position, before adding otheriweldmetal to fill the groove.

The arrangementindieated inl Fig. 3 may be applied to the welding ofcurved plates,as in the weldingA of longitudinalfand circumferentialseams 'in' tubular bodies, particularly :whenV the diameters are largeenough to permit access to the interior for positioning and adjustingthe block carrier |30 and its supports |32, since Without change in theform of the Welding groove. the variation entails merely minor changesin the shape or contour of the block |28 and carrier |30 appropriate tothe curvature of the plates as will be readily understood by thoseskilled in the art without detailed description and illustration. Forthe longitudinal scams in'smaller sized tubular .bodies it may be founddesirable to utilize the apparatus of Figs. 1 and 2, with minoradaptations to suit the longitudinal direction of welding, thepositioning and adjustingmechanisms remaining substantially the same.

The invention as herein disclosed in accordance with the provisions ofthe statutes will be understood by persons skilled in the art to beapplicable in arrangements other than those specifically described, andto include features which may be used vto advantage without acorresponding use of other features, within the scope of the appendedclaims.

We claim:

1. In a butt-welding process for joining the ends of ferrous metalplates or sections by metal fused within a welding groove defined` byand completely separating said ends, `backing said groove with anon-metallic non-slag-forming material more refractory to the heat ofwelding than the metal of the parts to be welded, applying metal powderto the interior of said groove in a relatively shallow layer continuousfrom wall to wall of said groove and confined to the base portion ofsaid groove in contact with said backing material, said powderconsisting solely of substantially pure ferrous metal, applying weldingheat to the upper surface of said layer to melt said powder and therebyform a pool of said relatively pure ferrous metal extending from wall towall of said .groove so as to exclude slag from within the base portionof said groove below `the surface of said pool, combining from aseparate source above said surface additional molten metal with saidpool metal to form a slag-free layer of weld metal joining said parts atthe lowermost portion of said welding groove, and continuing formationof the weld between said ends by fusion-depositing other additional weldmetal Within said groove to unite with said initially formed layer.

2. In a butt-Welding process for joining ferrous metal plates orsections at their ends by metal fused within a welding groove dened byand completely Separating said ends, backing said groove with asubstantially rigid mass presenting a non-slag-forming surface of carbonto the work. applying metal powder to the interior base portion of saidgroove against said carbon backing surface in a relatively shallowcontinuous layer extending from Wall to wall of said groove, said powderconsisting solely of substantially pure iron, maintaining an electricare above said layer of powder between a consumable electrode and thework to initially melt said powder throughout at least the upper surfacethereof so as to forma pool of substantially pure molten iron extendingfrom wall to wall of said groove and constituting a barrier toentrapment within the base portion of Said groove of slag resulting fromthe fusion of said electrode, the maintenance of-said arc causingfusion-deposited Weld metal from said elec.. trode to combine with themolten metal of -sald pool to form the initial layer of weld metaluniting said plates or sections, and continuing formation of the weldbetween said ends by causing additional weld metal deposite-d from saidelectrode to become fused with said initially formed layer,

3. In a butt welding process for joining ferrous metal components havingends formed and arranged to provide a welding space therebetween withlips on sai-d components partially closing said space at its base,bridging said space at the underside of said lips to inhibit the escapeof materials from said space, filling the bottom of said space with aporous layer of finely divided metal to a depth restricted to the baseportion of said space while covering the adjacent upper portions of saidlips, said finely `divided metal consisting solely of substantially pureferrous metal, applying welding heat locally to the exposed uppersurface of said finely divided metal to form a molten metal surfaceacross the width of the space between said lips and thereby exclude fromthe restricted sub-surface portion of said space slag resulting from thefusion of materials including metal of said components, and depositingmolten weld metal from a fusible weld rod onto said molten surface toform the initial layer of weld metal joining said components, theporosity of said mass retarding penetration of welding heat throughoutsaid mass so as to maintain said upper surface molten for floating saidslag during the deposition of said wel-drod metal.

4. In a butt-welding process for joining ferrous metal components havingends formed and arranged to provide a welding space therebetween withlips on said components partially closing said space at its base,bridging said space at the underside of said lips with a substantiallyrigid mass more refractory to the heat of welding than the metal of saidcomponents and presenting a nonslagging surface to the work, providing achannel in said bridging mass surface in alignment with the spacebetween said lips, filling said channel and the bottom portion of saidwelding space including said inter-lip space with a porousl layer offinely divided metal to a depth restricted to the base portion of saidspace while covering the adjacent upper portions of said lips, saidfinely divided metal consisting solely of a ferrous metal having amelting point high enough to compare with that of pure iron, maintainingan electric arc above said layer between a consumable electrode and thework to initially melt said finely divided metal throughout at least theupper surface of said layer so as to form a. molten metal surface acrossthe width of the space between said lips and thereby exclude from therestricted sub-surface portion of said space slag resulting from thefusion of materials including metal of said components, and depositingmolten weld metal from said electrode onto said molten surface to formthe initial layer of weld metal joining said components.

5. ln a butt-Welding process for joining ferrous metal parts by metalfused within a welding space defined by and completely separatingjuxtaposed surface portions of said parts, the steps of forming theinitial layer of wel-d metal joining said parts which comprise, backingsaid space with a substantially rigid mass so as to inhibit the escapeof materials from said space, filling the base portion of sai-d spaceadjacent said mass solely with finely divi-ded ferrous metal arranged ina relatively shallow continuous layer extending from wall to wall ofsaid space, maintaining a zone of welding heat above and exposed to theupper surface of said layer so as to melt said finely divided metalthroughout at least said surface and there.- by form a pool of saidferrous metal extending from wall to wall of sai-d space, and causingadditional metal to be rendered molten by said heat at a position abovesaid pool and to be deposited within sai-d space in uniting relationshipto said molten pool metal to form the initial layer of weld metaljoining said parts.

EVAN F, WILSON,

JOHN C. GR'UBB.

FLOYD A. FOWLER.

REFERENCES CITED The following references are of record in the file ofthis patent:

UNITED STATES PATENTS Number Name Date 379,453 DeBenardos Mar. 13, 18881,351,445 Smith Aug. 31, 1920 1,435,919 Fay Nov. 21, 1922 1,599,927Stresau Sept. 14, 1926 1,782,316 Robinoff et al Nov. 18, 1930 1,810,005Burnish June 16, 1931 1,902,051 Wall Mar. 21, 1933 1,962,350 Kane June12, 1934 1,964,926 Moss July 3, 1934 1,990,077 Kershaw Feb. 5, 19352,145,009 Keir Jan. 24, 1939 2,241,572 Armstrong May 13, 1941 2,279,044Heist Apr. 7, 1942 2,281,070 Jennings Apr. 28, 1942 2,294,650 BechtleSept. 1, 1942 2,326,865 Kennedy Aug. 17, 1943 2,331,689 Hodge Oct, 12,1943 2,348,728 Crecca May 16, 1944 2,352,716 Jones July 4, 19442,395,723 Chmielewski Feb. 26, 1946 FOREIGN PATENTS Number Country Date835,479 France Sept. 26, 1938 OTHER REFERENCES Steel, May 4, 1942, page78.

